IBFM-CNR, Segrate, Milan, Italy.
J Nucl Med. 2013 Jul;54(7):1106-12. doi: 10.2967/jnumed.112.111120. Epub 2013 May 22.
Hypoxic regions are present in different types of cancer and are a negative prognostic factor for disease progression and response to therapy. (18)F-fluoroazomycin-arabinofuranoside ((18)F-FAZA) and (64)Cu-diacetyl-bis(N4-methylthiosemicarbazone) ((64)Cu-ATSM) have been widely used to visualize hypoxic regions in preclinical and clinical studies. Although both these radioligands have high signal-to-noise ratios, (64)Cu-ATSM may be suitable for use in in vivo imaging and as a radiotherapeutic agent. Despite encouraging results suggesting that it may have a role as a prognostic tracer, (64)Cu-ATSM was recently shown to display cell line-dependent kinetics of oxygen-dependent uptake. We set out to evaluate the kinetics of (64)Cu-ATSM distribution in different cancer models, using (18)F-FAZA as the gold standard.
(18)F-FAZA and (64)Cu-ATSM uptake were compared ex vivo using dual-tracer autoradiography and in vivo using PET in different xenograft mouse models (FaDu, EMT-6, and PC-3). (18)F-FAZA uptake was compared with (64)Cu-ATSM uptake in PET studies acquired at early (2 h after injection) and delayed time points (24 h after injection). To evaluate the presence of hypoxia and copper pumps, the tumors from animals submitted to PET were harvested and analyzed by an immunohistochemical technique, using antibodies against carbonic anhydrase IX (CAIX) and copper pumps (Ctr1 and ATP7B).
(64)Cu-ATSM showed a higher tumor-to-muscle ratio than did (18)F-FAZA. In the FaDu mouse model, radioactivity distribution profiles were overlapping irrespective of the hypoxic agent injected or the time of (64)Cu acquisition. Conversely, in the EMT-6 and PC-3 models there was little similarity between the early and delayed (64)Cu-ATSM images, and both the radiotracers showed a heterogeneous distribution. The microscopic analysis revealed that (18)F-FAZA-positive areas were also positive for CAIX immunostaining whereas immunolocalization for copper pumps in the 3 models was not related to radioactivity distribution.
The results of this study confirm the cell-dependent distribution and retention kinetics of (64)Cu-ATSM and underline the need for proper validation of animal models and PET acquisition protocols before exploration of any new clinical applications.
缺氧区域存在于不同类型的癌症中，是疾病进展和对治疗反应的预后不良因素。（18）F-氟代氮杂胞苷（（18）F-FAZA）和（64）Cu-二乙酰基双（N4-甲基硫代半卡巴腙）（（64）Cu-ATSM）已被广泛用于临床前和临床研究中观察缺氧区域。尽管这两种放射性配体都具有较高的信噪比，但（64）Cu-ATSM 可能更适合用于体内成像和作为放射治疗剂。尽管有令人鼓舞的结果表明它可能作为预后示踪剂发挥作用，但（64）Cu-ATSM 的氧依赖性摄取动力学最近显示出与细胞系相关的依赖性。我们着手评估（64）Cu-ATSM 在不同癌症模型中的分布动力学，使用（18）F-FAZA 作为金标准。
使用双示踪剂放射自显影术在体外比较（18）F-FAZA 和（64）Cu-ATSM 的摄取，并在不同的异种移植小鼠模型（FaDu、EMT-6 和 PC-3）中使用 PET 在体内进行比较。在 PET 研究中，在早期（注射后 2 小时）和延迟时间点（注射后 24 小时）采集（18）F-FAZA 摄取与（64）Cu-ATSM 摄取进行比较。为了评估缺氧和铜泵的存在，对接受 PET 的动物的肿瘤进行了收获，并使用针对碳酸酐酶 IX（CAIX）和铜泵（Ctr1 和 ATP7B）的抗体进行免疫组织化学技术分析。
（64）Cu-ATSM 比（18）F-FAZA 具有更高的肿瘤与肌肉比值。在 FaDu 小鼠模型中，无论注射的缺氧剂如何，或（64）Cu 采集的时间如何，放射性分布曲线都是重叠的。相反，在 EMT-6 和 PC-3 模型中，早期和延迟（64）Cu-ATSM 图像之间几乎没有相似之处，两种示踪剂均表现出不均匀的分布。显微镜分析显示，（18）F-FAZA 阳性区域也对 CAIX 免疫染色呈阳性，而 3 种模型中的铜泵免疫定位与放射性分布无关。
本研究结果证实了（64）Cu-ATSM 的细胞依赖性分布和保留动力学，并强调在探索任何新的临床应用之前，需要对动物模型和 PET 采集方案进行适当的验证。
